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Petrological, Mineralogical and Geochemical Constraints on Hydrocarbon Bearing North Sea Reservoir ChalkNormal access

Authors: E.I. Kallesten, U. Zimmermann, M.V. Madland and M.W. Minde
Event name: IOR 2017 - 19th European Symposium on Improved Oil Recovery
Session: Poster Introductions 1
Publication date: 24 April 2017
DOI: 10.3997/2214-4609.201700300
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 8.6Mb )
Price: € 20

rved with SEM varies and there is a clear decrease in porosity stratigraphically downwards, along with more cementation and compaction. X-ray diffraction confirms calcite as most abundant in the whole-rock composition, with quartz and few other non-carbonate minerals like smectite, illite and kaolinite present. The silica content varies highly from <2 wt% in the shallower cores to 6 – 8 wt% in areas close to tight zones and up to 11 wt% in the deeper cores. δ13C and δ18O are lower than the secular global isotopic values for this period. Since similar disturbed stable isotope values are seen in other hydrocarbon-rich samples unexposed to any fluid for IOR purposes, the disturbance is assigned to a post-depositional diagenetic overprint, or to the influence of a secondary fluid of unknown origin, rather than the effect of the cores´ flooding status. Given the compositional variety of the Ekofisk reservoir rocks, selecting a single on-shore exposure as a standard equivalent for the Ekofisk chalk would be problematic. The complexity of the reservoir chalk and consideration of many other IOR influencing parameters, compel caution when transferring results from the onshore chalk modeling to the reservoir chalk (e.g. Hjuler and Fabricius, 2009). Beside the mineralogical composition of chalk strongly influencing compaction, the palaeo-environmental conditions at the time of deposition, the diagenetic history, calcite recrystallization and fossil preservation may affect the strength of the rock. Hence, a further thorough geological study on the reservoir chalk is necessary to verify the prospect of comparisons based on geological grounds.

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